Automatic transmissions for bicycles are not a new idea. One that many of you may remember is the Browning transmission, which was licensed by Suntour in the 80’s. More recently, Shimano’s Coasting group featured automatic 3-speed shifting, but like the Browning transmission, it was not really a commercial success. Those are just two of many automatic bicycle ideas that have come and gone in the past roughly hundred years, so why, you might ask, should we expect Nuvinci Harmony, a new automatic shifting system designed for the growing e-bike market, to fare any better?

I have been excited about the NuVinci continuously variable planetary (CVP) drivetrain since I first saw it in early 2007. After trying a NuVinci equipped bike at Interbike in 2009, I was even more convinced that the system provided a user-friendly shifting experience for ‘non-enthusiast’ cyclists, many of whom are new to bicycling altogether. To me, the addition of an auto-shifting version of the NuVinci N360 drivetrain makes perfect sense, especially for the e-bike market. The NuVinci CVP system has no gear steps, so a rider can maintain a steady cadence as the transmission automatically adjusts to changes in terrain, wind, road surface, etc. As the bike shifts variably, the rider won’t feel an abrupt difference, or hear a ‘clunk’ to remind them that the bike is shifting. Instead, the riding experience will be simple…just pedal and enjoy the feeling of riding a bike. For anyone who wants to shift manually, the Harmony system offers that option at the push of a button. The rider can choose “push button (automatic-only) shifting with three cadence settings (typically slow – medium – fast)” or manual twist shifting, making this system much more versatile than past automatic transmissions for bicycles.

Weight has been one of the recurring concerns that I have heard about the NuVinci hub. Even though the newer N360 hub weighs 30% less than their older model, it is still heavy compared to something like an Alfine 11 hub. Personally, I don’t think that weight difference matters all that much on a transportation/utility-oriented bike. On an e-bike though, 800 grams of extra weight is even less significant.

I expect to hear a few negative comments about automatic shifting from some of the hardcore cyclists out there, for whom shifting a bike is already second nature. If your first thought is “how hard is it to click a lever or twist a grip”, this product is probably not for you (of course, you are probably not in the market for an e-bike either). Yes, bicycle gearing is pretty simple, but many people who don’t ride regularly are still confused about when to shift, especially with a traditional derailleur set-up. It’s not that they can’t learn how to shift effectively, but some of them just don’t want to. More cars are sold with automatic transmissions than manual for that same reason. Sure, there is a still market for stick shift cars (for the record, I have one), but the average driver just doesn’t want to think about anything more than pressing the gas and brake pedals. An electric assist bike that can be easily pedaled at a comfortably even cadence might appeal to some of those “blue ocean” potential cyclists out there, for whom understanding the workings of even a simple transmission system holds no interest at all.

You can check out the Harmony press release and data sheet (pdf) on the NuVinci website for more information about the system. Also, Byron from Bike Hugger started an interesting discussion about it on his Google+ page, so I encourage you to take a look there as well. I am curious to hear what you all think about the Harmony system, so let me know in the comments.

11 Comments

Agreed that this on an E-Bike is going to be a powerful combo. Even as an experienced cyclist, I enjoy autoshifting… I was using a Shimano 4-speed autoshift system recently and really appreciated having one less thing to think about while negotiating the oft-disrespected NYC bike lanes.

Hmm, as you said, I’m not their target market. I also have a 1967 Jaguar E type with a four speed manual transmission. Your assessment may well prove accurate, particularly if cost premiums can be kept reasonable.

Without mention of an e-bike price equipped with this, I’m going to go ahead and assume it will cost more than a scooter (and possibly even more than a solid motorcycle), and thus quickly fail to find a market. It is a nifty enough idea, because I cycle enough to know I do have a preferred RPM for long rides that it would be sweet to just dial in and go, but all the overhead involved is going to kill the efficiency of the bike more than the fuss of manual shifting costs.

I will look more seriously at these things when some company steps away from the marketing and crunches the numbers to show a real benefit. I’m not going to double the weight of my bike and quintuple the price just to get a small electric boost without having to shift gears. I’d rather drop that money on something I didn’t have to pedal at all, which is already what most people do.

That’s not so horrible, all things considered. Still, though, I’d have to compare the e-bike to the lighter regular bike you can get at 1/3 the cost (and without all the extra electric parts to maintain). I really don’t think it’s asking too much to get solid numbers that compare input RPM to output speed (and corresponding distance on one charge). Maybe the Harmony systems will make it easier to market e-bikes that way.

I just want to be able to say, before I plunk down $3k, “Alright, the effort that would normally having me going 10mph will now have me going 20mph and the charge would still last 50 miles, which is more than enough to get me back and forth to work without being all sweaty. Sold!” Right now it’s mostly, “Meh, I’ll just split the difference and go 15mph on my lighter current setup.”

On the contrary: It will greatly benefit efficiency on ebikes since high torque is reduced because of this system. And high motor torque is exactly what eats up battery life. So as a result the range of the bike increases wich is the main focal point for most consumers

I think the main focal point for most consumers is “Will this help me sit on a couch and eat while watching TV.” Which is to say, I’ve seen no indication that e-bikes are getting people to ride who wouldn’t otherwise ride. Regular bikes are pretty damn cheap and efficient for anyone who is willing to go riding in the first place, so the niche that e-bikes really have to hit does not seem like the one they are marketing towards.

I only took one test ride on an autoshift bike and didn’t much care for it. The problem was hills (not even steep ones): in order to get the transmission to understand it should downshift, you gotta ease up on the pedaling… but that’s something you’re loath to do when going uphill because you’ll lose momentum. I felt that autoshift was counterintuitive and inefficient, a self-defeating proposition. Of course, pedelec makes this a much smaller problem than it is on a regular bike.

That makes me all the more curious about the NuVici Harmony though, as I imagine that this problem disappears with CVT. I can see the appeal of e-bikes for some… if you look at the number of old Dutch couples taking tours on the countryside riding e-bikes, you can imagine that there’s a market for CVT-autoshift-pedelec machines. I could probably sell my fairly sedentary parents on those, too.

NuVinci is a CVT that is expected to minimize energy loss on changing gear-ratios and the gear-shift is smooth, as ‘nicolas’ pointed above.

On the other hand, NuVinci is a sort of Traction Drive. Traction drive is usually unfamiliar even to mechanical engineers and mostly regarded as a magic to not-engineers. In a traction drive, flat-surfaced rollers contact with other flat-surfaced rollers without teeth. And amazingly the rollers transfer power without slippage.

The secret of this magic is from the lubricant called ‘traction oil’. Traction oil dramatically increases friction at contact-surfaces of rollers : Imagine a bicycle having two steel wheels but no rubber tires on them. The bicycle is running on a large steel plate. Yes, there will be slippages whenever high pedaling torque is given. But if traction oil is covered on the steel plate then No Slip.

What I hope to note is ‘operating conditions’ of the drive. Transferring high torque without slippage needs high friction and it’s possible by increasing contact pressure between rollers. High friction causes high energy loss. So a traction drive is known to be suitable for relatively low torque & high speed conditions. ※ All experimental studies on traction drives what I saw described their input speed is over 1000rpm(mostly around 1500rpm).

The NuVinci maker will not reveal the efficiency. ※ I guess the minimum efficiency could be under 85%. Most people can’t feel such amount of energy loss on rides because the rolling resistances of tires are bigger.

Anyway it doesn’t mean NuVinci is useless. NuVinci is a surely good invention providing differentiated characteristics. I think the drive is effective but (just) not efficient.

My friends and I are currently designing a non-electric automatic shifting bicycle that uses the Nuvinci N360 rear hub. We’d love to have any interested parties take the bike for a spin and give us your honest feedback so we can try and improve the product. We are located in Michigan.